builtin-am: implement committing applied patch

Implement do_commit(), which commits the index which contains the
results of applying the patch, along with the extracted commit message
and authorship information.

Since 29b6754 (am: remove rebase-apply directory before gc, 2010-02-22),
git gc --auto is also invoked to pack the loose objects that are created
from making the commits.

Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/am.c

@@ -11,6 +11,9 @@
 #include "run-command.h"
 #include "quote.h"
 #include "lockfile.h"
+#include "cache-tree.h"
+#include "refs.h"
+#include "commit.h"
 
 /**
  * Returns 1 if the file is empty or does not exist, 0 otherwise.
@@ -673,11 +676,57 @@ static int run_apply(const struct am_state *state)
 	return 0;
 }
 
+/**
+ * Commits the current index with state->msg as the commit message and
+ * state->author_name, state->author_email and state->author_date as the author
+ * information.
+ */
+static void do_commit(const struct am_state *state)
+{
+	unsigned char tree[GIT_SHA1_RAWSZ], parent[GIT_SHA1_RAWSZ],
+		      commit[GIT_SHA1_RAWSZ];
+	unsigned char *ptr;
+	struct commit_list *parents = NULL;
+	const char *reflog_msg, *author;
+	struct strbuf sb = STRBUF_INIT;
+
+	if (write_cache_as_tree(tree, 0, NULL))
+		die(_("git write-tree failed to write a tree"));
+
+	if (!get_sha1_commit("HEAD", parent)) {
+		ptr = parent;
+		commit_list_insert(lookup_commit(parent), &parents);
+	} else {
+		ptr = NULL;
+		fprintf_ln(stderr, _("applying to an empty history"));
+	}
+
+	author = fmt_ident(state->author_name, state->author_email,
+			state->author_date, IDENT_STRICT);
+
+	if (commit_tree(state->msg, state->msg_len, tree, parents, commit,
+				author, NULL))
+		die(_("failed to write commit object"));
+
+	reflog_msg = getenv("GIT_REFLOG_ACTION");
+	if (!reflog_msg)
+		reflog_msg = "am";
+
+	strbuf_addf(&sb, "%s: %.*s", reflog_msg, linelen(state->msg),
+			state->msg);
+
+	update_ref(sb.buf, "HEAD", commit, ptr, 0, UPDATE_REFS_DIE_ON_ERR);
+
+	strbuf_release(&sb);
+}
+
 /**
  * Applies all queued mail.
  */
 static void am_run(struct am_state *state)
 {
+	const char *argv_gc_auto[] = {"gc", "--auto", NULL};
+
 	refresh_and_write_cache();
 
 	while (state->cur <= state->last) {
@@ -709,16 +758,14 @@ static void am_run(struct am_state *state)
 			exit(128);
 		}
 
-		/*
+		do_commit(state);
-		 * NEEDSWORK: After the patch has been applied to the index
-		 * with git-apply, we need to make commit as well.
-		 */
 
 next:
 		am_next(state);
 	}
 
 	am_destroy(state);
+	run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
 }
 
 /**